|Fig. 1: Nuclear Reactor. (Source: Wikimedia Commons)|
Nuclear energy has always been a source of confusion and mistrust, since it is most widely known for weapons of mass destruction and the creation of a giant lizard. The situation is further exacerbated by the few yet high-profile incidents such as Chernobyl, Fukushima and Three Mile Island. However, the majority of nuclear energy development is towards clean sources of energy with greatly reduced risk compared to fossil fuels. This report seeks to investigate the magnitude of energy produced by nuclear reactors (Fig. 1) and report the values in more familiar terms, while also comparing the dangers to the widely used fossil fuels. Converting meaningless numbers into something more relatable will hopefully clear up some of the confusion, better informing attitudes and decisions towards this promising energy source.
Nuclear energy is generated from the splitting of atoms, where the energy holding the chemical bonds together is released along with high-speed particles that trigger further splitting reactions. Nuclear power plants usually use uranium-235, a type of uranium which is easier to split. The energy is released in the form of heat which is used to drive processes typical of power plants that generate electricity, such as converting water to steam.  At the end of 2015, global capacity of nuclear energy generation reached 382.9 gigawatts with 441 operational reactors, with each reactor contributing around 1 gigawatt on average.  The US residential sector consumed 4230 trillion Btu over 10 months in 2016, which is around 14.1 trillion Btu/day.  With around 135 billion housing units it comes down to around 104 Btu/day per household.  1 gigawatt is around 82 billion Btu/day, which means that a single nuclear reactor can provide around 82 billion houses with clean energy. Another interesting number to look at is the world's consumption of nuclear in terms of tonnes oil equivalent. In 2015, almost 600 million tonnes oil equivalent of nuclear energy were consumed globally, meaning nuclear energy took the place of burning 600 billion kg of oil.  The abundance of uranium fuel makes nuclear energy extremely suitable for large-scale continuous power production, and is seen as integral to solving the energy crisis in the future.
Radiation is usually the public's biggest concern, since people run the risk of contacting radioactive material during accidents involving the plant or transportation of waste, and even during routine plant operations. However, nuclear plants are designed with several layers of safety nets, which kick in one after the other in case of failure in the previous level. It would require the failure of all backup systems for any exposure to occur. Typical probabilistic safety analysis show that "a fuel meltdown might be expected once in 20,000 years of reactor operation. In 2 out of 3 meltdowns, there would be no deaths, in 1 out of 5 there would be over 1,000 deaths, and in 1 out of 100,000 there would be 50,000 deaths. The average for all meltdowns would be 400 deaths."  While 400 seems to be an unacceptable number, it is important to keep in mind the time span is over 20,000 reactor years of operation. As a comparison, "particle pollution from [fossil fuel] power plants is estimated to kill approximately 13,000 people a year," which would require there to be over 30 meltdowns every year for nuclear energy to be as dangerous.  The combined radioactivity from these exposures factoring in the probability of accidents occurring is around 0.2% of exposure from natural radiation. Since 1% of cancers is caused by natural radiation, exposure from nuclear technology is responsible for an eventual 0.002% increase in cancer risk, the equivalent of less than an hour loss of life expectancy. In contrast, burning fossil fuels is estimated to be 3-40 days loss of life expectancy. 
Given the low probability of accidents, explanations are necessary for Chernobyl, Fukushima and Three Mile Island. In the case of Chernobyl, the accident was caused by a combination of poorly designed reactors and multiple safety violations during the course of a rushed experiment without any reactor experts on hand. Such an accident would never happen under the strict regulations and requirements today, or even at the time in the US. Unstable reactors without proper containment cannot be licensed, regulations are strictly enforced, no unrelated experimentation is allowed using reactors, reactors are designed to stop uncontrolled chain reactions and water prevents the spread of radioactive material in all accident scenarios. It is also important to note that while being the worst nuclear power accident, only 31 lives were lost at Chernobyl and those most exposed to radiation had a 4% increase in their chance of dying from cancer. More lives are lost daily in occupational hazards in the US. Fukushima suffered from natural disasters beyond what it was designed to handle. Although the reactors were successfully shutdown when the earthquake hit, the cooling system did not have sufficient time to remove the residual heat before the subsequent tsunami caused the backup power to fail. Analysis shows Fukushima's implemented protection was insufficient, with inadequate physical protection from tsunami and poor placement of backup power supply. While the resulting explosion injured about a dozen people, the plant was stabilized and exposure managed within accepted emergency levels. No lives were lost. Plant requirements against natural disasters have since then been further developed. Finally, Three Mile Island was the only major nuclear accident that occurred in the US. In this case, at least two equipment failures were severely compounded by human errors. Despite this, two lines of defense remained intact and the radioactivity was completely contained. No casualties resulted and the incident can be counted as a successful demonstration of layering defenses. One final thought to keep in mind is that there were only three major accidents in 15,000 reactor years that stretch to when nuclear energy regulations were still in their infancy. 
Nuclear energy has made great progress in terms of energy produced as well as safety regulations. Nuclear power plants are designed with many contingencies in place, even against major natural disasters or targeted attacks. With only three major accidents to date, and only one of them in the US (which was completely contained), it is important to evaluate the apparent threat of nuclear energy against currently accepted forms of energy. In all cases, nuclear energy does not pose as much risk or cause as much harm as power plants burning fossil fuels. In exchange, it provides clean energy from an abundant fuel source, something much needed in our struggle to become carbon neutral. Educating the public and demystifying this arcane form of energy that has been so often used as the bogeyman by the media is therefore of the utmost importance.
© Wayne Sheu. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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